The present application relates to a device and methods for connecting elongated surgical members, and in particular, to methods and connectors that allow elongated surgical members of different materials to be attached together while inhibiting galvanic corrosion.
It is often necessary to surgically treat disorders such as scoliosis and broken bones with two or more elongated surgical members. The elongated members, typically either rods or plates, are placed along the area to be treated, such as the broken bone or the vertebral column. The elongated members may be attached with various attachment devices, such as screws, hooks, and various other types of fasteners.
It is well known that the strength and stability of a dual member assembly can be increased by coupling the members with a connector that transversely connects to the longitudinal axes of the members. Specifically, the two members are parallel to each other and may overlap, or may be in an end-to-end configuration.
Biocompatible materials are used for the members but, however, due to corrosion concerns, members of different materials are rarely connected together. The corrosion resistance commonly referred to in the art is against direct chemical attack, which in the body means a slow erosion of the material by acids which dissolve the material. It is well known that most body fluids that bathe implants are acidic. The biocompatible metals dissolve extremely slowly in the body. Polymers are even more resistant to acidic attack.
A second type of corrosion is electro-chemical, also called galvanic corrosion. Every metal is conductive and has a distinct electro-chemical potential, i.e., voltage when immersed in an acidic or saline environment. A battery is created when two such metals are introduced in a common bath, and then connected together. One metal becomes an electron donor and dissolves, and the other becomes an electron receptor and adds material (a compound of the donor and the bath materials). Galvanic corrosion is a serious problem when metals of different galvanic potential are combined in a common medium and in close proximity to each other.
Generally, galvanic corrosion is avoided by using members of only one type of metal. However, this limits the choice of a plurality of metals of different properties when desired, such as stress resistance, elasticity, hardness, and so forth. Further, if two different members are close to one another, a battery action can be made if there is some contact, such as anchors and plates and so forth.
Therefore, devices and methods are needed that would allow the elongated surgical members to be connected together while inhibiting galvanic corrosion.